ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Silver as anode in cryolite—alumina-based melts

M. Kucharík, P. Chamelot, L. Cassayre, and P. Taxil

Institute of Inorganic Chemistry, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 36 Bratislava, Slovakia

E-mail: uachkuch@savba.sk

Received: 9 August 2006  Revised: 7 November 2006  Accepted: 8 November 2006

Abstract: The anodic behaviour of silver was investigated in cryolite—alumina-based melt. Silver has a lower melting point (ca. 960°C) than the other metals considered as possible inert materials for aluminium electrolysis. The working temperature used in aluminium industry is approximately 960°C, depending on the melt composition. Therefore, the stability of silver during the anodic process was tested at 870°C in an acidic electrolyte consisting of 65.5 mass % Na₃AlF₆ + 22.9 mass % AlF₃ + 5.7 mass % CaF₂ + 3.9 mass % LiF + 2 mass % Al₂O₃ with the melting point ca. 850°C. The electrolyte without alumina was prepared as well, with the melting point ca. 860°C. The resulting cryolite ratio (CR = n(NaF)/n(AlF₃)) for both electrolytes was equal to 1.6. The behaviour of the silver anode was studied by voltammetry measurements. The electrochemical study showed that an oxidation reaction occurred at a potential below the oxygen evolution potential. Silver was not found to be stable under oxygen evolution. The degradation of the silver anode was apparent after electrolysis.

Keywords: silver electrode - cryolite - alumina - low-temperature electrolyte

Full paper is available at www.springerlink.com.

DOI: 10.2478/s11696-007-0011-x

Chemical Papers 61 (2) 142–145 (2007)